1. Field of the Invention
This invention relates to a vulcanizing metal mold for vulcanizing and molding raw tires and, specifically, to a metal mold for vulcanizing tire treads, which is constituted by a plurality of sector molds for molding treads of tires. More particularly, the invention relates to a metal mold for vulcanizing tire treads, capable of preventing incorrect assembling of a plurality of pieces attached to a casing for molding a tread pattern.
2. Description of the Related Art
A metal mold of the type split in the circumferential direction has heretofore been known as a metal mold for vulcanizing the tires. The metal mold of this type is provided with many apertures called vent holes for venting the air communicated with the interior and exterior of the metal mold to discharge a gas such as the air trapped between the metal mold and the raw tire out of the metal mold while the tire is being vulcanized. However, the vent holes are formed through a step of forming many vent holes in the metal mold. Besides, the spews that are cut often remain in the vent holes.
To overcome the cumbersome maintenance of the above metal mold, JP-A-5-200753 discloses a metal mold for vulcanizing tires in which many segment pieces are formed by turning an aluminum alloy material forming a tread-molding portion necessary for forming a tire pattern and cutting and splitting it in the circumferential direction, and many segment pieces are assembled on the inside of a holder made of iron, the many segment pieces being held maintaining such a gap that permits the passage of the air but blocks the rubber.
Even with the metal mold split into the pieces, however, the rubber adheres on the surfaces of the metal mold and in the air-venting gaps among the pieces like the ordinary metal mold for vulcanizing the tires after the tires are vulcanize-molded several hundreds to several thousands of times, impairing the appearance of the obtained tires and lowering the venting effect, still requiring the washing of the metal mold at regular intervals.
As for the tread patters of the tires, on the other hand, the pitch of pattern is differed in a state of maintaining similar patterns that are to be formed, usually, dividing the circumferential length of the tire into not less than 50 pitches while employing not less than three kinds of pitches in order to suppress vibration and noise of the tire while traveling. Therefore, the split pieces having different pattern pitches must be regularly arranged adjacent to each other in the metal mold for molding the tread. At the time of assembling the metal mold after the washing, therefore, the split pieces must be very carefully arranged to prevent incorrect assembling, which is a time-consuming work.
Therefore, JP-A-7-314459 is proposing a metal mold for vulcanizing tires, which facilitates easy and quick washing of the metal mold and assembling of the metal mold.
In order to prevent incorrect assembling of the split pieces, so far, characters for identification have been engraved at positions other than the surface for forming the tread enabling the pieces to be rearranged by making sure the characters but still inviting the chances for incorrectly arranging the pieces.
Further, according to JP-A-7-314459, the pieces can be positioned, but incorrect assembling cannot be confirmed until after the pieces are set in the casing. Besides, limitation is imposed on the direction for inserting the pieces in the casing, still leaving room for improvement.